In order to reduce friction and wear in mechanically interacting surfaces a lubricant is introduced to the zone of interaction. As described schematically in FIG. 1A to which reference is now made, under ideal lubricating conditions, the lubricant film 20 between the surfaces 32 and 34, moving at relative velocity V, forms an intact layer which permits the moving surfaces to interact with the lubricant. Under such conditions, no contact between the Interacting surfaces 32 and 34 occurs at all, the lubricant layer is said to carry the load P existing between the interacting layers. If the supply of lubricant is insufficient, a reduction in the effectivity of the lubrication ensues, which allows surface to surface interactions to occur.
As described schematically in FIG. 1B to which reference is now made, below a certain level of lubricant supply, the distance between the moving surfaces 32 and 34 diminishes because of load P, the asperities of the surfaces, which are the peaks of surface material protruding from the surfaces, may mutually interact. Thus, for example, the asperity 36 of surface 34 of a machine part, can form physical contact and interact with the asperity 38 of surface 32. The asperities of surfaces 32 and 34 carry all of the load existing between the interacting surfaces. In such a condition, often referred to as boundary lubrication, the lubricant is ineffective and the friction and wear are high.